Numerous different mechanisms are used in today's lives for communication. A communication made using one of these mechanisms is referred to herein as a call. Mechanisms used include standard telephone calls mobile and fixed line, internet or network based calls typically using voice over Internet Protocol, VoIP, video-phone calls, chat sessions text based or otherwise, and application-sharing sessions when an application on a single machine can be controlled by two users, one of whom is on a remote machines. You can see it in action using MSN Messenger and other similar packages.
All of the mechanisms have at least three phases that occur in sequence:                Initiation phase;        Communication phase; and,        Termination phase.        
Whilst the initiation and termination phases will include transmission of data that could be considered “communication”, the communication phase referred to in this document is intended to refer to the (typically synchronous) interaction between users once a call has been initiated by one party and accepted by another.
The termination phase includes resource recovery, billing and the like. This phase is not particularly relevant to the present invention and therefore is not described further.
The initiation phase is triggered by a party requesting the call (referred to hereafter as the “originator”) and accepted by at least one other party (referred to hereafter as a “recipient”). Typically, once the originator requests his or her system to initiate a call, a connection is established with the recipient's system via data communication referred to as a “handshake”. Handshakes are typically transparent to the originator and recipient and dealt with by the underlying communication mechanisms. During the handshake, the originator's and recipient's systems and any necessary intermediate systems exchange data necessary for the communication phase to start. In connection-oriented communications, the handshake stage may also include negotiation of necessary facilities such as bandwidth with intermediate systems to support and route data during the communication phase.
When the recipient's system receives a handshake, an appropriate notification is typically provided to alert the recipient of the requested call. The recipient accepts the call in the manner appropriate to the communication system (picking up the phone, pressing a button, accepting a prompt from a user interface etc.). The manner of notification typically depends on the nature and facilities of the recipient's system and any customisation or personalisation that has been applied. For example, the recipient's system may pick a particular ring tone to be played when a call is received, an icon to be displayed, an action to be performed such as vibrate in mobile telephones or some combination thereof.
The initiation phase of standard fixed line voice calls, made over PSTN or ISDN systems, involves the sending of a call-setup packet of data usually referred to as the Calling Line Identifier CLI, although it contains more information than just the telephone number of the originating system, to the recipient's system. During the transmission of the CLI, switches within the telephone network are configured to establish an end-to-end connection. There are variations to the format of the call-setup data on different systems, although these are largely interoperable.
Mobile telephone networks, such as those based on GSM, CDMA or UMTS systems, use the same CLI formats as fixed lines. However, due to the technology needed to establish a wireless connection, mobile telephones tend to be much more sophisticated than fixed line telephones. One use of mobile to telephone is to enable a recipient to associate a particular notification type with one or more originator's CLI, for example so that a call from one originator is notified with a different ring tone to that of another originator.
VoIP systems are very varied in the way in which they are implemented, but the usual approach has an initiation phase in which the originating and recipient systems exchange a small amount of data in a format defined by a set of rules, often using the standardised Session Initiation Protocol SIP.
IP technology allows text-based chat, video-calls and the use of shared graphical environments. With respect to session initiation, these are all implemented in the same way as VoIP.